Abstract A method and apparatus for controlling a vehicle
engine. A catalyst 56 in the exhaust system for reducing
NOx emissions. When the catalyst 56 is full, the air-fuel
mixture is temporarily enriched for reducing the level of
NOx. A primary control procedure regulates torque
fluctuation or other characteristic during normal operation.
For example, the primary control procedure may control the
intake air. During the primary control procedure, a
coefficient is determined, based on the operating state of
the engine, to control the output characteristic. When the
catalyst 56 is full, a temporary control procedure varies
the fuel-air ratio to increase the level of hydrocarbons
delivered to the catalyst 56, which reduces the NOx. The
temporary control procedure regulates the amount of fuel
injected based on the same coefficient used in the primary
control procedure. Therefore, the output characteristic is
substantially unchanged by the temporary control procedure.
The primary control procedure regulates torque fluctuation
in one embodiment, and the coefficient may be based on the
position of the throttle valve, the position of the EGR
valve or the quantity of fuel injected into the combustion
chambers 5. In another embodiment, the primary control
procedure is for controlling the ignition timing, and the
temporary control procedure uses a coefficient based on the
timing retardation determined in the primary control
procedure.
An engine including a combustion chamber (5) for
burning air-fuel mixture and an exhaust passage (55) for
discharging the burned gases, the engine being operated
under a primary control procedure, wherein the primary
control procedure controls torque fluctuation or knocking,
the engine being characterized by: a catalyst (56) in the exhaust passage (55) for
storing nitrogen oxides contained in the exhaust gas and for
reducing the level of emitted nitrogen oxides; a detector (101, 102, 105) for detecting an engine
operation state for the primary control procedure; a determiner (103) for determining whether to change
the air-fuel ratio of the air-fuel mixture, based on the
state of the catalyst; and a controller (104, 105, 106, 107) for temporarily
changing the air-fuel ratio based on the decision of the
determiner, wherein the fuel supplied to the combustion
chamber during the temporary change of the air-fuel ratio is
based on the detected engine operation state, which is
determined and used in the primary control procedure, so
that the nitrogen oxides stored in the catalyst (56) will be
reduced.
Claim 2
Dependent Claim
24 words
The engine according to claim 1 characterized by that
the controller changes the air-fuel ratio so that an engine
output characteristic remains substantially unchanged.
Claim 3
Dependent Claim
40 words
The engine according to claim 2 characterized by that
the controller has a map that is referred to when changing
the air-fuel ratio, wherein the map includes coefficients
for compensating the air-fuel ratio in accordance with the
primary control procedure.
Claim 4
Dependent Claim
44 words
The engine according to claim 1 characterized by that
the primary control procedure determines at least one of a
fuel supply amount, air intake amount, exhaust gas
recirculation amount and ignition timing, and wherein the
controller changes the air-fuel ratio based on the
determination.
Claim 5
Dependent Claim
45 words
The engine according to claim 1 characterized by that
the determiner calculates the amount of nitrogen oxides
stored in the catalyst (56) and determines whether to change
the air-fuel ratio when the amount of nitrogen oxides
exceeds a predetermined storage amount of the catalyst (56).